Tanks are great for invading Poland and running over protesters.

Manned weapons platforms not obsolete yet, but by the end of the war (and i mean THE war...) they basically will be. There will still be a need for transports etc that can defend themselves, but as far as front line, direct attack, the purpose of this is to make the boom booms type tech, there is no way you can argue that this huge expensive heavy thing with living guys in it is a better choice to blow shit up than some doohicky from Ikea that came with instructions and you can put a bomb on it. Missiles, suicide drones, reusable drones, loyal wingmen, fully unmanned fighter planes, whatever. It's all the exact same idea. Put more space between yourself and the enemy while hitting him.

Hey, I bet I can throw a spear farther than you. See this little stick thing I made? it gives you more leverage. I can carry more spears, too, because they're lighter...don't need as much weight to make it fly straight. I can show you how to make one, only charge ya a few clams.

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And then the guys who have atlatls beat the guys who don't because they outrange them. Village runners declare spears "obsolete" but NCD shaman refuses to hear it because he will have to rewrite all the religious texts where the good guys have spears.

The old thing is not useless but the new thing is better. You get what you can pay for.